Zero concentration gradient

A discussion forum for users of the new HYDRUS 2D/3D. HYDRUS is a software package for simulating water, heat and solute movement in two- and three-dimensional variably saturated media. Happy Posting!
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castanho
Posts: 4
Joined: Mon Dec 10, 2007 3:22 pm

Zero concentration gradient

Post by castanho » Tue Oct 25, 2011 5:52 pm

Dear all

How do i assign to the bottom of a 3D object a zero concentration solute gradient? What kind of boundary condition in the window should i select? This boundary is a free drainage flux for water movement.
Thanks
Paulo

Jirka
Posts: 4620
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Post by Jirka » Tue Oct 25, 2011 7:31 pm

Simply select the third-type (or concentration flux) boundary conditions. This boundary conditions is automatically changed to the zero gradient (Neumann) boundary condition at the outflow boundary (such as for Free Drainage (except for the Atmospheric boundary).

J.

castanho
Posts: 4
Joined: Mon Dec 10, 2007 3:22 pm

Post by castanho » Wed Oct 26, 2011 4:23 pm

Dear Prof. Jirka Thanks for the fast answer.I suspected that but was not sure.
I have two more questions about the solute boundary condition.
a) I try to simulate the solid urea fertilization. Spread the fertilizer in the first cm of the soil, so I have no flux, I've got is a concentration, so i have first type boundary condition. Am I right?
b) I simulate 180 days but in the first day i make the total input of urea (pulse duration - 1 day, and the i input the concentration in the first day at variable condition Hydrus window. Am I right?
Thanks and Best Regards
Paulo

Jirka
Posts: 4620
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Post by Jirka » Wed Oct 26, 2011 6:36 pm

HYDRUS does not simulate solid phase solutes and their dissolution. Thus likely the best scenario for you is to specify solute to be initially in the profile using the initial condition. If your solute is in both liquid and adsorbed phae, in version 1, you need to adjust the liquid phase concentration so that the total mass is correct. In version 2 you can use the option "Initial condition specified in total concentration [Mass_solute/Volume_soil]", to do these adjustments for you. In every case, see the Mass Balance Information, to make sure that you have a correct mass in the profile, and if needed adjust your input.

iaelr
Posts: 12
Joined: Tue Aug 12, 2014 1:52 pm
Location: USA

Re: Zero concentration gradient

Post by iaelr » Thu Nov 15, 2018 11:42 pm

Hi Jirka,

I am wondering if there has been any changes regarding solid application of fertilizer/solutes in the newer Hydrus versions.
As well as Paulo, I am trying to simulate solid application of fertilizer to the soil.
As you suggested here, solid fertilizer can be added in the initial condition, but I am simulating multiple seasons.

Thank you,
iael

Jirka
Posts: 4620
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

Re: Zero concentration gradient

Post by Jirka » Fri Nov 16, 2018 1:42 am

There have been no changes in HYDRUS in how the initial and boundary conditions are handled. Chemical compounds can enter the soil profile only in the liquid form (i.e., dissolved in water). J.

iaelr
Posts: 12
Joined: Tue Aug 12, 2014 1:52 pm
Location: USA

Re: Zero concentration gradient

Post by iaelr » Fri Nov 16, 2018 5:35 pm

Thanks!

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